Plasmonic Dimers Research Articles

Heating Effects on Nanofabricated Plasmonic Dimers with Interconnects

Plasmonic nanostructures with electrical connections have potential applications as new electro-optic devices due to their strong light–matter interactions. Plasmonic dimers with nanogaps between adjacent nanostructures are especially good at enhancing local electromagnetic (EM) fields at resonance for improved performance. In this study, we use optical extinction measurements and high-resolution electron microscopy imaging to investigate the thermal stability of electrically interconnected plasmonic dimers and their optical and morphological properties. Experimental measurements and finite difference time domain (FDTD) simulations are combined to characterize temperature effects on the plasmonic properties of large arrays of Au nanostructures on glass substrates. Experiments show continuous blue shifts of extinction peaks for heating up to 210°C. Microscopy measurements reveal these peak shifts are due to morphological changes that shrink nanorods and increase nanogap distances. Simulations of the nanostructures before and after heating find good agreement with experiments. Results show that plasmonic properties are maintained after thermal processing, but peak shifts need to be considered for device design.

DNA origami-mediated plasmonic dimer nanoantenna-based SERS biosensor for ultrasensitive determination of trace diethylstilbestrol

Diethylstilbestrol (DES) is a threatening factor to the human endocrine system. Here, we reported a DNA origami-assembled plasmonic dimer nanoantenna-based surface-enhanced Raman scattering (SERS) biosensor for measuring trace DES in foods. A critical factor influencing the SERS effect is interparticle gap modulation of SERS hotspots with nanometer-scale accuracy. DNA origami technology aims to generate naturally perfect structures with nano-scale precision. Exploiting the specificity of base-pairing and spatial addressability of DNA origami to form plasmonic dimer nanoantenna, the designed SERS biosensor generated electromagnetic-enhancement and uniform-enhancement hotspots to improve sensitivity and uniformity. Owing to their high target-binding affinity, aptamer-functionalized DNA origami biosensors transduced the target recognition into dynamic structural transformations of plasmonic nanoantennas, which were further converted to amplified Raman outputs. A broad linear range from 10−10 to 10−5 M was obtained with the detection limit of 0.217 nM. Our findings demonstrate the utility of aptamer-integrated DNA origami-based biosensors as a promising approach for trace analysis of environmental hazards.

Plasmon-Mediated Hydrogen Dissociation with Symmetry Tunability.

The atomic-scale mechanism of plasmon-mediated H2 dissociation on gold nanoclusters is investigated using time-dependent density functional theory. The position relationship between the nanocluster and H2 has a strong influence on the reaction rate. When the hydrogen molecule is located in the interstitial center of the plasmonic dimer, the hot spot here has a great field enhancement, which can promote dissociation effectively. The change in the molecular position results in symmetry breaking, and the molecular dissociation is inhibited. For the asymmetric structure, direct charge transfer from the gold cluster to the antibonding state of the hydrogen molecule by plasmon decay makes a prominent contribution to the reaction. The results provide deep insights into the influence of structural symmetry on plasmon-assisted photocatalysis in the quantum regime.

Non-amplification on-spot identifying the sex of dioecious kiwi plants by a portable Raman device.

The kiwi plant is dioecious, and its sex is generally identified from flower morphology at blossoming, which takes several years. It is quite necessary but challenging to on-spot identify the plant sex in juvenile stage. Here the target DNA was obtained by screening the Friendly boy (FrBy) gene which is sex-related for different kiwi plant species. Its complementary sequence was divided into two parts as primer DNA and further attached to different gold nanoparticles (GNPs). The connection between target DNA and primer DNA will promote the formation of plasmonic dimers. Dark field microscopy (DFM) can distinguish particles in different aggregation states. Various conditions were optimized based on the standard of increasing the proportion of dimers while reducing that of large aggregates. Furthermore, two Raman reporters (RR) are separately labeled on the nanoprobes, and the plasmonic dimers lead to a tremendous Raman enhancement of two reporters located at the dimer nanogap. Double-blind tests proved the feasibility of this method on the actual samples of kiwi plant leaves. Our SERS method is sensitive, specific, and reliable for rapid sex identification analysis at the kiwi seeding stage, with great promise for decision-making in field management.

Position and Orientation dependent Hybridization and Energy transfer of Dipole Emitter around Plasmonic Homodimers

AbstractA dipole emitter (analogous to organic molecules) placed near any dielectric or metal nanoparticles, based on their spatially constrained location and orientation, vividly emulate optical nanoantennas. Herein, we have extensively simulated the single dipole emitter interaction with spherical homodimers of noble metal gold and silver nanoparticles for different positional dependent orientations, exemplifying systematically the hybridization (Rabi splitting), quenching and diffuse non‐radiative energy transfer effects. The blue‐shifted scattering spectra of the coupled dipole emitter with individual Ag and Au homodimers quantify and corroborate the corresponding quantum yield/efficiency estimations. Such spatially oriented emitter interaction further distinctly reveals the enhanced near‐field and far‐field effects of the plasmonic dimer system in terms of dipolar and quadrupolar resonances, arising due to the induced polarization by respective incident electric and opto‐magnetic field components. Understanding the surface‐enhanced behavior of organic molecules that are either incorporated or randomly attached (experimentally) on the surface of metal nanoparticles will benefit greatly from the present comprehensive data analysis.

Nonlinear chaotic dynamics in nonlocal plasmonic core-shell nanoparticle dimer.

Plasmonic nanoparticles can be employed as a promising integrated platform for lumped optical nanoelements with unprecedentedly high integration capacity and efficient nanoscale ultrafast nonlinear functionality. Further minimizing the size of plasmonic nanoelements will lead to a rich variety of nonlocal optical effects due to the nonlocal nature of electrons in plasmonic materials. In this work, we theoretically investigate the nonlinear chaotic dynamics of the plasmonic core-shell nanoparticle dimer consisting of a nonlocal plasmonic core and a Kerr-type nonlinear shell at nanometer scale. This kind of optical nanoantennae could provide novel switching functionality: tristable, astable multivibrators, and chaos generator. We give a qualitative analysis on the influence of nonlocality and aspect ratio of core-shell nanoparticles on the chaos regime as well as on the nonlinear dynamical processing. It is demonstrated that considering nonlocality is very important in the design of such nonlinear functional photonic nanoelements with ultra-small size. Compared to solid nanoparticles, core-shell nanoparticles provide an additional freedom to adjust their plasmonic property hence tuning the chaotic dynamic regime in the geometric parameter space. This kind of nanoscale nonlinear system could be the candidate for a nonlinear nanophotonic device with a tunable nonlinear dynamical response.

Single-Step Plasmonic Dimer Printing by Gold Nanorod Splitting with Light.

Optical printing is a flexible strategy to precisely pattern plasmonic nanoparticles for the realization of nanophotonic devices. However, the generation of strongly coupled plasmonic dimers by sequential particle printing can be a challenge. Here, we report an approach to generate and pattern dimer nanoantennas in a single step by optical splitting of individual gold nanorods with laser light. We show that the two particles that constitute the dimer can be separated by sub-nanometer distances. The nanorod splitting process is explained by a combination of plasmonic heating, surface tension, optical forces, and inhomogeneous hydrodynamic pressure introduced by a focused laser beam. This realization of optical dimer formation and printing from a single nanorod provides a means for dimer patterning with high accuracy for nanophotonic applications.

Numerical study of magneto-optical binding between two dipolar particles under illumination by two counter-propagating waves

Introduction: The formation of a stable magneto plasmonic dimer with THz resonances is theoretically studied for the principal directions of the system. Unlike a recent report, our work provides a complete description of the full photonic coupling for arbitrary magnetic fields as, for instance, unbalanced particle spins.Methods: As an illustration, we consider two small, n-doped InSb nanoparticles under illumination by two counter-propagating plane waves.Results: Remarkably, when an external magnetic field exists, the symmetry in the system is broken, and a resonant radiation pressure for the dimer appears. Similarly, tunable inter-particle forces and spins are exerted on the non-reciprocal dimer. The system is also characterized when the magnetic field is absent. Moreover, we show how the mechanical observables truly characterize the dimer since their resonance dependency contains detailed information about the system.Discussion: Unlike far-field observables like absorption, mechanical magnitudes depend on the system's near-field. In addition, the nature of the particle spins is originally explained by the energy flow's behavior around the dimer. This work constitutes a generalization of any previous approach to optical binding between small nanoparticles. It paves the way for fully controlling optical matter and nano factory designs based on surface plasmon polaritons.

Nanowire dimer optical antenna brightens the surface defects of silicon

Abstract Plasmonic hot spots located between metallic dimer nanostructures have been utilized comprehensively to achieve efficient light emission. However, different from the enhancement occurred in the plasmonic hot spot, the investigation of light emission off the hot spot on submicron scale remains challenge. In this work, we have constructed a plasmonic nanowire dimer (NWD) system to brighten the light emission of the surface defects of silicon off the hot spot on the submicron scale. The NWD can trap light through plasmonic gap, then, the excited emitter on the submicron scale can radiate light efficiently by coupling with the dipole gap plasmonic mode. Furthermore, the coupling of dipole plasmonic mode with the emitters can be tuned by changing the gap size, and then photoluminescence emission was drastically enhanced up to 126 folds. Theoretical simulations reveal the photoluminescence enhancement arises from the combination of the NWD’s high radiation efficiency, Purcell enhancement, efficient redirection of the emitted photoluminescence and the excitation enhancement. In this study, the photoluminescence signal can be effectively enhanced by placing nano-antenna patch on the detected low-quantum-efficiency emitters, which may open up a pathway toward controlling plasmonic gap mode enhanced light emission off the hot spot on submicron scale.

Boosting Light–Matter Interaction in a Longitudinal Bonding Dipole Plasmon Hybrid Anapole System

Achieving strong electromagnetic enhancement is critical for realizing strong light–matter coupling at the nanoscale. In this study, we constructed a hybrid anapole system composed of a nanohole silicon disk and a longitudinal bonding dipole plasmon mode-supported plasmonic dimer. Compared with the bare dimer plasmon, the hybrid system shows strong plasmonic resonance tuning ability, and its resonance peak can be tuned to the near-infrared region only by adjusting the radius of the silicon disk. Meanwhile, the E-field enhancement in the gap region can exceed four orders of magnitude without sacrificing the quality factor of the system. Furthermore, it is demonstrated that the emitter’s radiative decay rate enhancement in the hybrid system is much higher than that of a similar LBDP mode-supported plasmonic dimer nanodisk and the reported plasmonic nanocavity. In summary, our hybrid anapole systems combine the advantages of metal plasmonic nanodimers and conventional anapole mode-supported systems and avoid their disadvantages. This study provides a useful reference for the further exploration of single-photon emission sources, light harvesting, and other quantum nanophotonic applications.

Surface roughness in finite-element meshes: application to plasmonic nanostructures

Photonic and plasmonic nanostructures almost unavoidably exhibit some degree of surface roughness for which the details depend on the fabrication process. A corresponding quantitative modeling thus requires the separation of numerical errors from the effects of roughness as well as the systematic construction of rough surfaces with prescribed properties. Here, we present a practical approach for constructing meshes of general rough surfaces with given autocorrelation functions based on the unstructured meshes of nominally smooth surfaces. The approach builds on a well-known method to construct correlated random numbers from white noise using a decomposition of the autocorrelation matrix. We discuss important details pertaining to the application of the approach for modeling of surface roughness and provide a corresponding software implementation. As an example application, we demonstrate the impact of surface roughness on the resonance frequencies and quality factors of a plasmonic nano-sphere dimer using an open-source boundary finite-element Maxwell solver. The approach can be utilized within a broad range of numerical methods to analyze the effects of surface roughness in various fields of science and engineering.

Gold Nanorod DNA Origami Antennas for 3 Orders of Magnitude Fluorescence Enhancement in NIR.

DNA origami has taken a leading position in organizing materials at the nanoscale for various applications such as manipulation of light by exploiting plasmonic nanoparticles. We here present the arrangement of gold nanorods in a plasmonic nanoantenna dimer enabling up to 1600-fold fluorescence enhancement of a conventional near-infrared (NIR) dye positioned at the plasmonic hotspot between the nanorods. Transmission electron microscopy, dark-field spectroscopy, and fluorescence analysis together with numerical simulations give us insights on the heterogeneity of the observed enhancement values. The size of our hotspot region is ∼12 nm, granted by using the recently introduced design of NAnoantenna with Cleared HotSpot (NACHOS), which provides enough space for placing of tailored bioassays. Additionally, the possibility to synthesize nanoantennas in solution might allow for production upscaling.

Early warning of Diaporthe infection in kiwifruit soft rot by plasmonic dimer-enhanced Raman spectroscopy.

Diaporthe genus is the dominant pathogens of kiwifruit soft rot with long incubation period and rapid onset and very hard to detect in advance. It is of great significance to develop point-of-care tests for disease prevention and field management. Here we screen a pair of genus-level primers for constructing plasmonic dimer Rayleigh/Raman spectroscopy, which enables rapid, specific, and sensitive detection of Diaporthe genus in real kiwifruits. Dark-filed Rayleigh scattering clearly visualizes the target-induced dimer assembly of nanoprobes. Plasmonic dimer-enhanced Raman spectroscopy has high specificity for 12 common isolates of Diaporthe genus in one batch samples with highly accurate results and much higher sensitivity than polymerase chain reaction (PCR). It realizes the recognition of Diaporthe infection at an early stage of 24h when the kiwifruits do not have any noticeable symptoms. It demonstrates a bright prospect of point-of-care tests for early warning of kiwifruit soft rot infection and quality control.

Broadband plasmonic switches based on nanodisc-dimers with progressively increasing diameters on a plasmonic film with a VO2 spacer

In this paper, we propose active broadband plasmonic switches based on a periodic array of metallic dimers of nanodiscs with progressively increasing diameters on a gold coated SiO 2 substrate with a VO2 thin film as a spacer between the nanodiscs and the underlying plasmonic substrate. Periodic arrays based on unit cells with plasmonic nanodisc dimers of varying diameters are employed to couple multiple wavelengths of the incident radiation into the plasmonic modes of the nanostructure, which results in a broadband plasmonic response. We employ a vanadium dioxide (VO2) thin film as a spacer between these periodic sets of plasmonic nanodisc-dimers and the underlying gold coated substrate to achieve broadband switching. On exposure to voltage, infrared light or heat, the VO2 spacer layer changes from its semiconducting state to its metallic state. This transformation leads to significant changes in its optical properties leading to changes in the reflectance spectra of the proposed nanostructure. This results in an efficient switching action over wide range of wavelengths spanning the C, L and U bands of optical communication. We demonstrate a broadband extinction ratio of 5 dB over an operating wavelength range of 650 nm spanning from 1460 nm to 2110 nm, and a broadband extinction ratio of 4 dB over an operating wavelength range of 702 nm spanning from 1432 nm to 2134 nm. In addition, we demonstrate the trade-off between the extinction ratio and the operating wavelength range of these switches. An exhaustive analysis of these switches has been carried out using finite difference time domain (FDTD) modelling to demonstrate that the spectral range over which switching can be achieved by employing these switches can be varied by varying the geometrical parameters of the proposed switches and thus these switches offer the flexibility of being employed for different wavelength regimes. These switches can be potentially employed in optical communication networks or as switching elements in plasmonic circuits.

Design of plasmonic enhanced all-optical phase-change memory for secondary storage applications

Phase-change optical device has recently gained tremendous interest due to its ultra-fast transmitting speed, multiplexing and large bandwidth. However, majority of phase-change optical devices are only devoted to on-chip components such as optical tensor core and optical main memory, while developing a secondary storage memory in an optical manner is rarely reported. To address this issue, we propose a novel phase-change optical memory based on plasmonic resonance effects for secondary storage applications. Such design makes use of the plasmonic dimer nanoantenna to generate plasmonic resonance inside the chalcogenide alloy, and thus enables the performance improvements in terms of energy consumption and switching speed. It is found that choosing height, radius, and separation of the plasmonic nanoantenna as 10 nm, 150 nm, and 10 nm, respectively, allows for a write/erase energies of 100 and 240 pJ and a write/erase speed of 10 ns for crystallization and amorphization processes, respectively. Such performance merits encouragingly prevail conventional secondary storage memories and thus pave a route towards the advent of all-optical computer in near future.

Non-Adiabatic Dynamics Simulation of Plasmon-Mediated Chemistry

Localized surface plasmon resonances (LSPRs) have attracted much recent attention for their potential in promoting chemical reactions with light. However, the mechanism of LSPR-induced chemical reactions is still not clear and suffers from many controversies. This presentation will discuss the atomic-scale mechanism of plasmonic hot-carrier mediated chemical reaction exampled by H2 dissociation by employing time-dependent density functional calculations theory and non-adiabatic molecular dynamics. The key observation is that there are nested excited states corresponding to both hot-electron excitation and charge transfer [1]. These nested states cross, facilitating the transitions depicted in the desorption induced by the electronic transitions model and the surface hopping model. I believe this is the first time that such a connection has been made based on a first-principles calculation. Diabatization of these states shows that the charge transfer states are responsible for H2 dissociation, while the hot electron states do not. Previous works only identified the hot electron states, thus were unable to explain the dissociation in a convincing way. Moreover, we also found chemical reaction is tunable if the molecule is placed in the center of the plasmonic dimer [2]. The reaction rate can be either suppressed or enhanced depending on the geometry.[1] Q. Wu, L. Zhou, G. C. Schatz, Y. Zhang*, H. Guo*, J. Am. Chem. Soc. 2020, 142, 13090–13101.[2] Y. Zhang*, T. Nelson, S. Tretiak, H. Guo, G. C. Schatz. ACS Nano, 2018, 12, 8415-8422.

Investigation of the fano lineshapes in plasmonic asymmetric silver nanosphere dimer

The plasmonic properties of an asymmetric dimer, comprising of two silver nanospheres with different radii, are studied by the finite difference time domain method. The extinction efficiencies of the plasmonic dimer are numerically calculated in the visible and near-infrared regime, i.e., from 950 to 150 THz. Two distinguishable Fano resonances are observed when the separation between the nanospheres is narrowed within a certain value, e.g., less than 10 nm. The extinction spectrum that presents two Fano resonances, associated with two electromagnetic modes, is well fitted using a model consisting of two Fano lineshape functions. The resonance frequencies, the spectral widths, and the characteristic q values are obtained via the best fit parameters, and their trends are revealed with varying the radii of the nanospheres. The fitting scheme proposed in this work may be useful in the study of other plasmonic nanostructures with multiple Fano resonances.

Plasmonic Gold Trimers and Dimers with Air-Filled Nanogaps.

The subwavelength confinement of light energy in the nanogaps formed between adjacent plasmonic nanostructures provides the foundational basis for nanophotonic applications. Within this realm, air-filled nanogaps are of central importance because they present a cavity where application-specific nanoscale objects can reside. When forming such configurations on substrate surfaces, there is an inherent difficulty in that the most technologically relevant nanogap widths require closely spaced nanostructures separated by distances that are inaccessible through standard electron-beam lithography techniques. Herein, we demonstrate an assembly route for the fabrication of aligned plasmonic gold trimers with air-filled vertical nanogaps having widths that are defined with spatial controls that exceed those of lithographic processes. The devised procedure uses a sacrificial oxide layer to define the nanogap, a glancing angle deposition to impose a directionality on trimer formation, and a sacrificial antimony layer whose sublimation regulates the gold assembly process. By further implementing a benchtop nanoimprint lithography process and a glancing angle ion milling procedure as additional controls over the assembly, it is possible to deterministically position trimers in periodic arrays and extend the assembly process to dimer formation. The optical response of the structures, which is characterized using polarization-dependent spectroscopy, surface-enhanced Raman scattering, and refractive index sensitivity measurements, shows properties that are consistent with simulation. This work, hence, forwards the wafer-based processing techniques needed to form air-filled nanogaps and place plasmonic energy at site-specific locations.

Freeze-Driven Adsorption of Poly-A DNA on Gold Nanoparticles: From a Stable Biointerface to Plasmonic Dimers.

Increasing attention is paid to poly-adenine (poly-A) DNA-functionalized gold nanoparticles due to the high cost of thiols. Freezing is an effective approach for immobilizing poly-A DNA on gold nanoparticles, but its mechanism remains elusive. To cope with this issue, in this paper, some experimental insights are provided. It is shown that (1) the DNA loading density is independent of the length of poly-A. (2) DNA is densely packed on gold nanoparticles, and the biointerface is peculiarly stable, which is not in line with the existing “wrapping” model. (3) Using a DNA-staining dye, thiazole orange, it is shown that poly-A duplex structures are formed on the surface of gold nanoparticles, with evidence given by fluorescence and Raman measurements. An alternative model involving stable poly-A duplexes anchored by finite terminal adenines is proposed. Based on it, a strategy for constructing plasmonic dimers is developed, using freeze-driven adsorption of a DNA sequence with poly-adenine at both ends. This work provides insights into the reaction between poly-A DNA and AuNPs upon freezing and is expected to facilitate related research in biosensor development and nanotechnology.

A systematic study of Surface Plasmon Enhanced Electric Field in Nanoparticle Dimers for UV Plasmonics

AbstractSurface plasmon mediated electric field enhancement in the dimer arrangement of Al, Ag and, Au nanoparticles using multipole spectral expansion (MSE) approach has been studied. MSE method has flexibility and simplicity in extending the approach to treat an arbitrary arrangement of nanoparticles by solving corresponding general eigenvalue problem. The field enhancement behavior of Al, Ag, and Au nanoparticle dimers has been investigated, covering UV–VIS spectral range. The role of embedding medium, particle–particle separation, and the metal type were studied. The resonance wavelength showed the red shift with increasing the dielectric constant of the ingrained material. The red shift with increasing particle size and the dielectric constant of embedded or ingrained medium has been studied. This study was used to design plasmonic nanoparticle dimer with resonant optical response at crucial wavelengths in UV–VIS spectral region.